Nautiloceras

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Nautiloceras is an extinct genus of nautiloid cephalopods in the order Nautilida. The Nautilida includes the living Nautilus and its close relative Allonautilus. Nautiloceras is poorly known and likely belongs to the family Trigonoceratidae. Some researchers consider Nautiloceras to be a junior synonym of Trigonoceras, a genus described by M’Coy.

Classification
- Kingdom: Animalia
- Phylum: Mollusca
- Class: Cephalopoda
- Subclass: Nautiloidea
- Order: Nautilida
- Genus: Nautiloceras D’Orbigny, 1849

Geologic age and range
- Fossils are usually dated to the Upper Tournaisian stage of the early Carboniferous, about 352–345 million years ago (Lower Osage).
- Some sources place the related Trigonoceras as slightly younger, in the Upper Viséan to Lower Serpukhovian, roughly 340–322 million years ago.

Shell shape
- Nautiloceras may have had a curved (cyrtoconic) shell or a loosely coiled (gyroconic) shell, with the whorls not in contact.
- Gyroconic shells may show a subtriangular cross-section with a broad, concave underside (venter) along the outer rim.

In short, Nautiloceras is an early Carboniferous nautiloid with uncertain taxonomy and limited fossil material.